Mortar projectile



Dec. 11, 1956 o, BONNER 2,773,450

MORTAR PROJECTILE Filed May 28, 1953 mmvrox [fans 0220 D011 ncr /61:}ghrlo hem:

United States Patent MORTAR PROJECTILE Hans Otto Donner, Tampere,Finland, assignor to Soltam Ltd., Haifa, Israel Application May 28,1953, Serial No. 357,944

Claims priority, application Finland April 18, .1953

3 Claims. (Cl. 102-93) This invention relates to new and usefulimprovements in trench and field mortar projectiles.

A trench or field mortar is a weapon for firing finstabilized ornon-spinning projectiles with some elevation, generally not less than40, from a barrel provided with an internal smooth bore, the lower orbreech end of which is adapted to be engaged by means of a ball orcardan type joint in a ribbed base plate which relays to the ground theshocks incident of firing and recoil. The muzzle part of the mortarbarrel is supported on a cradle provided with a coil spring assembly andadapted to be attached resiliently to a suitable bipod or tripodsupport.

Military weapons adapted to fire projectiles and impart thereto a speedof Mach number less than 1 are known. Recently, projectiles have beendeveloped which retain their stability between Mach numbers 1 and 1.3,but the firing range of these projectiles is limited by the fact thatthe fins, due to the resistance of air, tend to reduce the ballisticefliciency of the projectile by an amount roughly proportional to finthickness. This fin thickness cannot be reduced indefinitely for thereason that the fins must normally withstand the reaction forces ofturbulent gases developed in the barrel.

This invention has for its object to free the fins of the influence ofgases by the provision of a suitable obturating member to separate thefins entirely from the powder chamber proper.

The invention together with its object and advantages will best beunderstood from a study of the following description, taken inconnection with the accompanying drawing wherein a mortar grenadeembodying the invention is shown in principle.

The drawing illustrates a side view, partly in longitudinal section, ofa mortar projectile constructed in accordance with the presentinvention.

Referring to the drawing the projectile embodies the following mainparts and constructional details: a metallic main body 1 filled with anexposive charge and having a percussion cap 2 attached to the fore endthereof, a tail 3 on which suitable fins 4 are mounted. To the tubularpart 3 of the tail is secured a rearwardly conical thrust member 5having a frusto-conical outer surface tapering rearwardly and havingbored therein a longitudinal chamber 6 for an initial cartridge. Therear end of the thrust member 5 carries a member 7 for igniting theinitial cartridge and adapted to receive the flash charge. The member 5,moreover, is provided with radial passages 8 through which the gasesfrom the charge of explosive in the chamber 6 travel. About the member 5is arranged an obturating member 9 having a central rearwardly extendingextension 9 and provided with a central, rearwardly tapering passagewhich tapers at an angle smaller than that of the outer surface ofthrust member 5. This member 9 is provided with passages 8 correspondingto the radial passages 8 of the member 5. Moreover, the extension 9' ofthe member 9 has its inner wall contoured to define a cylindrical 2chamber 10 which via a passage 60, is in communication with the initialcartridge chamber 6 but has no passages leading away therefrom.

The greatest diameter of the obturating member 9 is slightly greaterthan the greatest diameter of the assemblage of fins and almost equal indiameter to the diameter of the internal bore of the mortar barrel.Hence, the mortar projectile made according to the teachings of thisinvention enters into the barrel along point 11 where the diameter ofthe member 9 is greatest. As shown in the drawing the member '9 isprovided at point 11 with two grooves 12 so the member 9 comprises threeseparate usually disc-like pieces of equal diameter for engaging thebore of the .barrel. The said grooves 12 are provided for the purpose ofpreventing gas pressure from being expanded past the space between thebarrel and the member 9 into the barrel part housing the projectilefins.

In the embodiment shown in the drawing the angle of the outer cone ofthe member 5 is greater than that of the known Morse projectile. On theother hand, the said angle should be so small as to preserve thestreamline shape of the projectile during its flight through the air, inconsequence of which the resistance of air decreases resulting in acorresponding increase in firing range of projectile. The member 9,provided with conical passages and arranged about the member 5 to pushthe said member 5 and consequently the whole projectile disposed withinthe barrel forward thereby imparting the required speed thereto, isadapted to be blown from the projectile immediately after the projectileis discharged from the barrel. This is eifected in the main by gaspressure developed in the chamber 10 by the initial cartridge, inconsequence of which the rear wall of said chamber recedes. Theresistance of air assists also in blowing the obturating member 9 fromthe member 5.

By use of the hereinabove described construction it is possible toreduce fin thickness to less than one fifth of that normally usedotherwise and thereby appreciably increase the firing range of theprojectile.

It is to be understood that while a specific form of the projectile hasbeen described for the purpose of illustration, other forms may beutilized with equal effect. For example, the tubular tail part 3 may beformed integral with the thrust member 5. Also, the body 1 may be madeintegral with the tubular part 3 to which is then secured the conicalmember 5 of light metal. The invention also contemplates an initialcartridge receiving chamber 6 so long as the same will project into thetubular tail part 3 in which case, however, the radial passages 8 arearranged to lead reaction gases developed by the initial cartridge intothe mortar barrel back of the obturating member 9.

Having thus described my invention, what I claim as new and desired tosecure by United States Letters Patent is: a

1. In a mortar projectile for discharge from a mortar and having fins onits rear end, a frusto conically shaped thrust member extendingrearwardly from the rear end of the projectile and having an internalcavity housing an initial charge, an obturating member removably mountedon said thrust member and having an outer diameter slightly greater thansaid fins and a reduced rearward extension surrounding said thrustmember, said thrust member and said rearward extension having radiallyaligned passages extending from said internal cavity for discharging theforces of the initial charge within the barrel to the rear of saidobturating member which is removed from said thrust member when theprojectile leaves the mortar barrel.

2. A mortar projectile according to claim 1, wherein Patented Dec. 11,1956 said obturating member has a diameter almost equal to the bore ofthe mortar barrel and its peripheral edge is provided with spacedcircumferential grooves.

3. A mortar projectile according to claim 1, wherein said obturatingmember and rearward extension have a central, rearwardly tapering boreextending therethrough and receiving said thrust member, and wherein thecone angle of said thrust member is greater than the angle of taper ofsaid bore of the obturating member and rearward extension so that saidthrust member is contacted only in the portion of said bore within saidobturating member, said rearward extension has an annular recess in thesurface of said bore defining a closed chamber surrounding and incommunication with the exterior surface of said thrust member, saidthrust member has a passageway connecting said chamber with saidinternal cavity containing the initial charge to cause said obturatingmember to be blown ofi the rear end of said thrust member by the forceof said initial charge entering said chamber through the last mentionedpassageway and as the projectile leaves the mortar barrel.

References Cited in the file of this patent UNITED STATES PATENTSBlacker Nov. 3, 1953

